I'm using C# WPF in Windows 10 Enterprise in Administrator user

I have a program that receives the file stored in binary form in SQL Server and puts it in a folder in the TEMP path. For example: there is a photo in the database, I select it and WriteAllBytes in the temp, then using Process.Start(C:\Users\ADMINI~1\AppData\Local\Temp.myiamge.png) I run that photo through the Windows Photo Viewer.

so for control the process has started to know when that would be ended I use this : MyProcess.WaitForExit(); but I get this error because MyProcess is null but it stated process successfully !

CS :

  string TempyPath = @"C:\Users\ADMINI~1\AppData\Local\Temp\tmpDCD8.2e0ea3b3-5b93-40f0-a227-40c85fd0a06b.png"; // return null Process
            string NormalPath = @"C:\tmpFB0A.5e2525f3-d4ef-4eb8-a920-c5c5b5d8402f.png";

//Test1
            var MyProcess0 = Process.Start(new ProcessStartInfo()
            {
                FileName = TempyPath,
                WindowStyle = ProcessWindowStyle.Maximized,
                UseShellExecute = true
            });
//Test2
            var MyProcess = Process.Start(TempyPath);
            MyProcess.WaitForExit();

            if (MyProcess.HasExited)
            {
                MessageBox.Show("You Cloes the Microsoft.Photos");
            }

Error for MyProcess.WaitForExit() :

System.NullReferenceException: 'Object reference not set to an instance of an object.'

MyProcess was null.

What should I do ?

Please guide me

Edit: I suspect three things:

1. File name
2. File path
3. Microsoft.Photos.exe Windows itself

What I need : How to open a file and after opening, wait until the window related to that opened file is closed (Control the status of the opened file in Windows)

CodePudding user response：

Process.Start returns null because when there is no new process started. An existing process is used to open the document instead of creating a new one.

If you really want to start a new process and wait for it to exit, then you should be explicit about which process to actually start:

var path = Environment.GetFolderPath(Environment.SpecialFolder.ProgramFiles);
var process = Process.Start(new ProcessStartInfo()
{
    FileName = "rundll32.exe",
    Arguments = string.Format(
        "\"{0}{1}\", ImageView_Fullscreen {2}",
        Environment.Is64BitOperatingSystem ?
            path.Replace(" (x86)", "") :
            path
            ,
        @"\Windows Photo Viewer\PhotoViewer.dll",
        TempyPath),
    WindowStyle = ProcessWindowStyle.Maximized,
    UseShellExecute = false
});

process.WaitForExit();

if (process.HasExited)
{
    MessageBox.Show("You Cloes the Microsoft.Photos");
}